U.S. patent application number 12/663602 was filed with the patent office on 2010-07-15 for silicone elastomers for high temperature performance.
Invention is credited to Igor Chorvath, Jon Vierling Degroot, JR., Michael Dipino, Robert Andrew Drake, David W. Lawson, Steven Robson, David Shawl, Lauren Marie Tonge.
Application Number | 20100179266 12/663602 |
Document ID | / |
Family ID | 39712065 |
Filed Date | 2010-07-15 |
United States Patent
Application |
20100179266 |
Kind Code |
A1 |
Chorvath; Igor ; et
al. |
July 15, 2010 |
Silicone Elastomers For High Temperature Performance
Abstract
Silicone elastomer base compositions containing a stabilizer are
disclosed that provide cured silicone elastomers having improved
high temperature performance. The stabilizer comprises carbon
black, calcium carbonate, iron oxide, and optionally zinc
oxide.
Inventors: |
Chorvath; Igor; (Midland,
MI) ; Degroot, JR.; Jon Vierling; (Midland, MI)
; Dipino; Michael; (North Branford, CT) ; Drake;
Robert Andrew; (Penarth, GB) ; Lawson; David W.;
(Cardiff, GB) ; Robson; Steven; (Vale of
Glamorgan, GB) ; Shawl; David; (Bay City, MI)
; Tonge; Lauren Marie; (Sanford, MI) |
Correspondence
Address: |
HOWARD & HOWARD ATTORNEYS PLLC
450 West Fourth Street
Royal Oak
MI
48067
US
|
Family ID: |
39712065 |
Appl. No.: |
12/663602 |
Filed: |
June 6, 2008 |
PCT Filed: |
June 6, 2008 |
PCT NO: |
PCT/US2008/066013 |
371 Date: |
December 8, 2009 |
Current U.S.
Class: |
524/425 |
Current CPC
Class: |
C08K 3/04 20130101; C08K
3/26 20130101; C08K 3/22 20130101; C08L 83/04 20130101; C08G 77/20
20130101; C08K 3/013 20180101; C08G 77/12 20130101; C08L 83/00
20130101; C08L 83/04 20130101; C08L 2666/54 20130101 |
Class at
Publication: |
524/425 |
International
Class: |
C08K 3/26 20060101
C08K003/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 8, 2007 |
US |
60933921 |
Dec 19, 2007 |
US |
61014907 |
Claims
1. A curable silicone elastomer composition comprising: A) 75-95 wt
% of a silicone elastomer base, B) 1.5-40 wt % of a stabilizer
comprising; B.sup.1) carbon black, B.sup.2) calcium carbonate,
B.sup.3) iron oxide, and B.sup.4) optionally zinc oxide, wherein
the amount by parts of components B.sup.1, B.sup.2, B.sup.3, and
B.sup.4 used in 100 parts of the stabilizer may vary from 2 to 50
parts, and C) 0-3 wt % of a cure agent, with the proviso that the
wt % of components A), B), and C) sums to 100 wt %.
2. The curable silicone elastomer composition of claim 1 wherein
the silicone elastomer base is a high consistency silicone rubber
base.
3. The curable silicone elastomer composition of claim 2 wherein
the high consistency silicone rubber base comprises; A.sup.1) an
organopolysiloxane comprising at least two unsaturated groups and
having a viscosity of at least 1000 mPas at 25.degree. C., A.sup.2)
a reinforcing filler, and A.sup.3) a filler treating agent.
4. The curable silicone elastomer composition of claim 1 wherein
the silicone elastomer base is a liquid silicone rubber.
5. The curable silicone elastomer composition of claim 4 wherein
the liquid silicone rubber comprises; A.sup.1) an
organopolysiloxane comprising at least two unsaturated groups and
having a viscosity of at least 1000 mPas at 25.degree. C., A.sup.2)
a reinforcing filler, A.sup.3) a filler treating agent, A.sup.4) an
organohydrogensiloxane having an average of greater than two
silicon bonded hydrogen atoms per molecule, and A.sup.5) a
hydrosilylation catalyst.
6. The curable silicone elastomer composition of claim 1 wherein
100 parts of the stabilizer contains 10 to 40 parts B.sup.1) carbon
black, 10 to 40 parts B.sup.2) calcium carbonate, and 10 to 40
parts B.sup.3) iron oxide.
7. A process for preparing a cured silicone elastomer comprising;
i) forming a mixture of the composition of claim 1 to a
configuration, and ii) vulcanizing the configured mixture, to
produce the cured silicone elastomer.
8. The cured silicone elastomer prepared by the process of claim
7.
9. The cured silicone elastomer of claim 8 wherein the cured
silicone elastomer has a tensile strength of at least 7 MPa and an
elongation of at least 200%.
10. The cured silicone elastomer of claim 8 wherein the tensile
strength of the cured silicone elastomer decreases by no more than
25 percent upon heat aging of the cured silicone elastomer for 7
days at 225.degree. C.
11. The cured silicone elastomer of claim 8 wherein; the tensile
strength of the cured silicone elastomer decreases by no more than
25 percent upon heat aging of the cured silicone elastomer for 7
days at 225.degree. C., and the elongation of the cured silicone
elastomer decreases by no more than 25 percent upon heat aging the
cured silicone elastomer for 7 days at 225.degree. C.
12. An article of manufacture comprising the cured silicone
elastomer of claim 8.
13. The article of manufacture of claim 12 wherein said article is
selected from O-rings, gaskets, seals, liners, hoses, tubing,
diaphragms, boots, valves, belts, blankets, coatings, rollers,
molded goods, extruded sheet, caulks, and extruded articles.
14. A method for improving the heat stability or heat resistance of
a silicone elastomer comprising: I) mixing a stabilizer with a
silicone elastomer base, said stabilizer comprising; B.sup.1)
carbon black, B.sup.2) calcium carbonate, B.sup.3) iron oxide, and
B.sup.4) optionally zinc oxide, II) vulcanizing the silicone
elastomer base containing the stabilizer.
15. The method of claim 14 wherein the silicone elastomer base is a
high consistency silicone rubber base.
16. The method of claim 14 wherein the silicone elastomer base is a
liquid silicone rubber base.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Application No.
60/933,921, as filed on 8 Jun. 2007, and to U.S. Application No.
61/014,907, as filed on 19 Dec. 2007.
TECHNICAL FIELD
[0002] This disclosure relates to silicone elastomer base
compositions containing a stabilizer that provide cured silicone
elastomers having improved high temperature performance. The
stabilizer comprises carbon black, calcium carbonate, iron oxide,
and optionally zinc oxide.
BACKGROUND
[0003] Automotive applications using silicone rubber are constantly
challenged to demonstrate performance improvements. Technology
trends result in demands for ever increasing resistance to both
heat and chemical exposure. For example, Western Europe continues
to exhibit significant growth in turbo diesel passenger cars, at
the expense of their gasoline equivalents. In the U.S., a similar
growth has been experienced in the small truck market. The service
temperatures and pressure of the hoses, especially turbo diesel
engine hoses, are thus increasing. Typically, the hoses used in
automotive applications have a multilayer structure consisting of
fabric reinforcement encapsulated with silicone rubber (classified
as VMQ elastomer by the American Society of Test Methods (ASTM))
and lined internally with a layer of fluoroelastorner (FVMQ).
[0004] There is a need to improve the heat stability of the
silicone elastomers used in automotive applications, and in
particular for their use in o-rings, connectors, and in the
construction of hoses.
[0005] The present inventors have discovered a stabilizer, that
when added to silicone elastomer base compositions, provide
improved heat aging properties to the cured silicone elastomer.
SUMMARY
[0006] This invention relates to a curable silicone elastomer
composition comprising: [0007] A) 75-95 wt % of a silicone
elastomer base, [0008] B) 1.5-40 wt % of a stabilizer comprising;
[0009] B.sup.1) carbon black, [0010] B.sup.2) calcium carbonate,
[0011] B.sup.3) iron oxide, and [0012] B.sup.4) optionally zinc
oxide, wherein the amount by parts of components B.sup.1, B.sup.2,
B.sup.3, and B.sup.4 used in 100 parts of the stabilizer may vary
from 2 to 50 parts, and [0013] C) 0-3 wt % of a cure agent, with
the proviso the wt % of components A), B), and C) sum to 100 wt
%.
[0014] In one embodiment, the curable silicone elastomer
composition contains a high consistency silicone rubber base
comprising; [0015] A.sup.1) an organopolysiloxane comprising at
least two unsaturated groups and having a viscosity of at least
1000 mPas at 25.degree. C., [0016] A.sup.2) a reinforcing filler,
and [0017] A.sup.3) a filler treating agent,
[0018] In another embodiment, the curable silicone elastomer
composition contains a liquid silicone rubber base comprising;
[0019] A.sup.1) an organopolysiloxane comprising at least two
unsaturated groups and having a viscosity of at least 1000 mPas at
25.degree. C., [0020] A.sup.2) a reinforcing filler, [0021]
A.sup.3) a filler treating agent, [0022] A.sup.4) an
organohydrogensiloxane having an average of greater than two
silicon bonded hydrogen atoms per molecule, and [0023] A.sup.5) a
hydrosilylation catalyst.
[0024] This disclosure also relates to the cured silicone elastomer
compositions and articles of manufacture prepared from them.
DETAILED DESCRIPTION
[0025] Component A) in the present disclosure is a silicone
elastomer base. As used herein, a "silicone elastomer base" is a
silicone composition when subsequently cured or vulcanized,
provides a silicone elastomer or rubber. Silicone refers to
organopolysiloxanes containing siloxane units independently
selected from (R.sub.3SiO.sub.0.5), (R.sub.2SiO), (RSiO.sub.1.5),
or (SiO.sub.2) siloxy units, where R may be any organic group.
These siloxy units can be combined in various manners to form
cyclic, linear, or branched structures.
[0026] The silicone elastomer base useful in component A) may be
selected from any silicone elastomer base known in the art, such as
those considered as high consistency silicone rubber bases. The
silicone elastomer base may also be selected from those considered
to be "liquid silicone rubber" compositions.
[0027] In one embodiment of the present disclosure, the silicone
elastomer base is a high consistency silicone rubber base. The high
consistency silicone rubber base may comprise; [0028] A.sup.1) an
organopolysiloxane comprising at least two unsaturated groups and
having a viscosity of at least 1000 mPas at 25.degree. C., [0029]
A.sup.2) a reinforcing filler, and [0030] A.sup.3) a filler
treating agent.
[0031] Component A.sup.1) is an organopolysiloxane comprising at
least two unsaturated groups and having a viscosity of at least
1000 mPas at 25.degree. C. The organopolysiloxane may have the
average composition of R.sup.1.sub.aSiO.sub.(4-a)/2. In which
R.sup.1 is selected from substituted and unsubstituted monovalent
hydrocarbon groups and is exemplified by alkyl groups such as
methyl, ethyl, and propyl, alternatively each alkyl group contains
from 1 to 10 carbon atoms, alternatively each alkyl group is a
methyl or ethyl group most preferably each alkyl group is a methyl
group; alkenyl groups such as vinyl, allyl, butenyl, and hexenyl;
aryl groups such as phenyl; and aralkyls such as 2-phenylethyl. The
average value of subscript a is from 1.95 to 2.05.
[0032] The organopolysiloxane of A.sup.1) has at least two
unsaturated groups and a viscosity of at least 1000 mPas at
25.degree. C. Typically, the unsaturated groups are alkenyl groups.
The alkenyl groups can be bonded in pendant positions, at the
terminal positions, or at both positions. The degree of
polymerization (dp) of such polymers is in the range of from 200 to
20,000.
[0033] The above dp range also includes polymers with a stiff
gum-like consistency which have a dp above about 1500 and have a
Williams plasticity number (ASTM D926) in the range of from about
30 to 250, and preferably from 95 to 125 (The plasticity number, as
used herein, is defined as the thickness in millimeters.times.100
of a cylindrical test specimen 2 cm.sup.3 in volume and
approximately 10 mm in height after the specimen has been subjected
to a compressive load of 49 Newtons for three minutes at 25.degree.
C.). Such gum-like polymers are generally used in compression or
transfer molds, calendaring, screw-type extruders or the like.
[0034] The organopolysiloxane can be a homopolymer or a copolymer
or a mixture of such polymers. The siloxy units comprising the
organopolysiloxane are exemplified by dialkylsiloxy groups wherein
each alkyl group may be the same or different, alkenylmethylsiloxy
groups where the alkenyl group contains from 2 to 10 carbon atoms,
preferably vinyl or hexenyl, and alkylphenylsiloxy wherein the
alkyl groups are as hereinbefore described. Any suitable terminal
groups in the organopolysiloxane may be utilised, examples include
trialkylsiloxy, and alkenyldialkylsiloxy groups wherein the alkenyl
and alkyl groups are as hereinbefore described. Examples of the
organopolysiloxane which may be used include
vinyldimethylsiloxy-endblocked dimethylsiloxane-vinylmethylsiloxane
copolymer, vinyldimethylsiloxy-endblocked polydimethylsiloxane,
vinylmethylhydroxysiloxy-endblocked
dimethylsiloxane-vinylmethylsiloxane copolymer, and
vinyldimethylsiloxy-endblocked
dimethylsiloxane-methylphenylsiloxane-vinylmethylsiloxane
copolymer.
[0035] The reinforcing fillers (A.sup.2) of the silicone elastomer
base are typically a silica. Many forms of silica are commercially
available such as fumed silica, precipitated silica, silica aerogel
and silica xerogel. Typically, the reinforcing silica filler has a
surface area of at least 100 m.sup.2/g and, alternatively, at least
200 m.sup.2/g. The reinforcing silica filler may be added in any
quantity which provides the desired reinforcement without adversely
affecting other properties of the elastomer. Generally, quantities
of 5-100 parts of reinforcing silica filler per 100 parts of
organosiloxane are useful.
[0036] Component (A.sup.3) is a filler treating agent (or a mixture
of treating agents) comprising an organopolysiloxane comprising at
least at least 2 hydroxy or otherwise hydrolysable groups, or a
mixture thereof and having an average degree of polymerisation of
from 2 to 50. Component (A.sup.3) may comprises units of the
formula R.sup.2.sub.aSiO.sub.(4-a)/2 in which R.sup.2 is selected
from substituted and unsubstituted monovalent hydrocarbon groups
and is exemplified by aryl groups such as phenyl groups or alkyl
groups such as methyl, ethyl, isopropyl, tertiary butyl and propyl,
alternatively each alkyl group contains from 1 to 10 carbon atoms,
more preferably each alkyl group is a methyl or ethyl group
alternatively each alkyl group is a methyl group. R.sup.2 may also
be selected from alkenyl groups such as vinyl, allyl and/or hexenyl
groups. The average value of subscript a is from 1.95 to 2.05. The
at least two hydroxy groups may be terminal hydroxy groups or
pendent groups on the chain or both. Each hydrolysable group may be
any suitable hydrolysable group which will interact with only
"cold" mixing with --OH groups on the hydrophilic filler surface.
Typically each hydrolysable group is an alkoxy group having from 1
to 10 carbon atoms or alternatively, if present the each alkoxy
group is a methoxy group or ethoxy group. The viscosity of
component (A.sup.3) is typically between 10 and 1000 mPas but may
be greater if required. The filler treating agent is typically
provided in an amount of from 0.5 to 0.12% by weight of the weight
of the filler (component (A.sup.2)).
[0037] Treating fillers results in improved room temperature
mechanical properties of the uncured compositions. Usually fillers
(component (A.sup.2) are treated in situ using an appropriate
treating agent or mixture thereof as described above. However the
filler(s) could be pre-treated if desired. Whilst a pre-treatment
step is generally avoided as it introduces an additional step into
the mixing process, pre-treated surface modified fillers, when
prepared, do not clump, and can be homogeneously incorporated into
the organopolysiloxane.
[0038] The silicone elastomer base may also include extending
fillers, such as titanium dioxide, quartz, magnesium oxide,
graphite, glass fibers and glass microspheres. The silicone
elastomer base may also include pigments, colorants, flame
retardants, additional heat stability additives, additives to
improve compression set and other additives commonly used in the
rubber art.
[0039] High consistency silicone rubber bases are known in the art,
and many are commercially available. Representative, non-limiting
examples include SILASTIC.RTM. GP 600 Silicone Rubber,
SILASTIC.RTM. New GP 600 Silicone Rubber, SILASTIC.RTM. HGS 701,
and SILASTIC.RTM. New HGS 701 Silicone Rubber.
[0040] In another embodiment, the silicone elastomer base is a
liquid silicone rubber. The liquid silicone rubber may have the
following composition; [0041] A.sup.1) an organopolysiloxane
comprising at least two unsaturated groups and having a viscosity
of at least 1000 mPas at 25.degree. C., [0042] A.sup.2) a
reinforcing filler, [0043] A.sup.3) a filler treating agent, [0044]
A.sup.4) an organohydrogensiloxane having an average of greater
than two silicon bonded hydrogen atoms per molecule, and [0045]
A.sup.5) a hydrosilylation catalyst. Components A.sup.1, A.sup.2,
and A.sup.3 are the same as described above.
[0046] Component (A.sup.4) is an organohydrogensiloxane having an
average of greater than two silicon bonded hydrogen atoms per
molecule. The organohydrogensiloxane contains an average of at
least two silicon-bonded hydrogen atoms per molecule, the remaining
valences of the silicon atoms being satisfied by divalent oxygen
atoms or by monovalent hydrocarbon radicals comprising one to seven
carbon atoms. The monovalent hydrocarbon radicals can be, for
examples, alkyls such as methyl, ethyl, propyl, tertiary butyl, and
hexyl; cylcoalkyls such as cyclohexyl; and aryls such as phenyl and
tolyl and/or trifluoroalkyl groups, e.g. trifluoropropyl groups or
perfluoroalkyl groups. Such materials are well known in the art.
The molecular structure of the organohydrogensiloxane may be
linear, linear including branching, cyclic, or network-form or
mixture thereof. There are no particular restrictions on the
molecular weight of the organohydrogensiloxane, however it is
preferable that the viscosity at 25.degree. C. be 3 to 10,000 mPas.
Furthermore, the amount of component (A.sup.4) that is added to the
composition is an amount such that the ratio of the number of moles
of hydrogen atoms bonded to silicon atoms to the number of moles of
alkenyl groups bonded to silicon atoms is in the range of 0.5:1 to
20:1, or alternatively in the range of 1:1 to 5:1.
[0047] The silicon-bonded organic groups present in the
organohydrogensiloxane can include substituted and unsubstituted
alkyl groups of 1-4 carbon atoms that are otherwise free of
ethylenic or acetylenic unsaturation. For the purpose of this
application "substituted" means one or more hydrogen atoms in a
hydrocarbon group has been replaced with another substituent.
Examples of such substituents include, but are not limited to,
halogen atoms such as chlorine, fluorine, bromine, and iodine;
halogen atom containing groups such as chloromethyl,
perfluorobutyl, trifluoroethyl, and nonafluorohexyl; oxygen atoms;
oxygen atom containing groups such as (meth)acrylic and carboxyl;
nitrogen atoms; nitrogen atom containing groups such as
amino-functional groups, amido-functional groups, and
cyano-functional groups; sulfur atoms; and sulfur atom containing
groups such as mercapto groups.
[0048] Component (A.sup.5) is a hydrosilylation catalyst. Typically
the hydrosilylation catalyst chosen may comprise any suitable
hydrosilylation catalyst such as a platinum group metal based
catalyst selected from a platinum, rhodium, iridium, palladium or
ruthenium catalyst. Platinum group metal containing catalysts
useful to catalyze curing of the present compositions can be any of
those known to catalyze reactions of silicon bonded hydrogen atoms
with silicon bonded alkenyl groups. Typically, the platinum group
metal for use as a catalyst to effect cure of the present
compositions by hydrosilylation is a platinum based catalyst.
Representative platinum based hydrosilylation catalysts for curing
the present composition include platinum metal, platinum compounds
and platinum complexes. Representative platinum compounds include
chloroplatinic acid, chloroplatinic acid hexahydrate, platinum
dichloride, and complexes of such compounds containing low
molecular weight vinyl containing organosiloxanes. Other
hydrosilylation catalysts suitable for use in the present invention
include for example rhodium catalysts such as
[Rh(O.sub.2CCH.sub.3).sub.2].sub.2, Rh(O.sub.2CCH.sub.3).sub.3,
Rh.sub.2(C.sub.8H.sub.15O.sub.2).sub.4,
Rh(C.sub.5H.sub.7O.sub.2).sub.3,
Rh(C.sub.5H.sub.7O.sub.2)(CO).sub.2,
Rh(CO)[Ph.sub.3P](C.sub.5H.sub.7O.sub.2),
RhX.sup.4.sub.3[(R.sup.3).sub.2S].sub.3,
(R.sup.2.sub.3P).sub.2Rh(CO)X.sup.4, (R.sup.2.sub.3P).sub.2Rh(CO)H,
Rh.sub.2X.sup.4.sub.2Y.sup.2.sub.4,
H.sub.aRh.sub.bolefin.sub.cCl.sub.d,
Rh(O(CO)R.sup.3).sub.3-n(OH).sub.n where X.sup.4 is hydrogen,
chlorine, bromine or iodine, Y.sup.2 is an alkyl group, such as
methyl or ethyl, CO, C.sub.8H.sub.14 or 0.5C.sub.8H.sub.12, R.sup.3
is an alkyl radical, cycloalkyl radical or aryl radical and R.sup.2
is an alkyl radical an aryl radical or an oxygen substituted
radical, a is 0 or 1, b is 1 or 2, c is a whole number from 1 to 4
inclusive and d is 2, 3 or 4, n is 0 or 1. Any suitable iridium
catalysts such as Ir(OOCCH.sub.3).sub.3,
Ir(C.sub.5H.sub.7O.sub.2).sub.3, [Ir(Z.sup.4)(En).sub.2].sub.2), or
(Ir(Z.sup.4)(Dien)].sub.2, where Z.sup.4 is chlorine, bromine,
iodine, or alkoxy, En is an olefin and Dien is cyclooctadiene may
also be used.
[0049] The hydrosilylation catalyst may be added to the present
composition in an amount equivalent to as little as 0.001 part by
weight of elemental platinum group metal, per one million parts
(ppm) of the composition. Typically, the concentration of the
hydrosilylation catalyst in the composition is that capable of
providing the equivalent of at least 1 part per million of
elemental platinum group metal. A catalyst concentration providing
the equivalent of 3-50 parts per million of elemental platinum
group metal is typically used.
[0050] Optional additives for a silicone liquid rubber composition
in accordance with the present invention may comprise one or more
of the following hydrosilylation catalyst inhibitors, rheology
modifiers, pigments, coloring agents, anti-adhesive agents adhesion
promoters, blowing agents, flame retardants, electrically and/or
thermally conductive fillers, and desiccants.
[0051] Any suitable platinum group type inhibitor may be used. One
useful type of platinum catalyst inhibitor is described in U.S.
Pat. No. 3,445,420, which is hereby incorporated by reference to
show certain acetylenic inhibitors and their use. A preferred class
of acetylenic inhibitors is the acetylenic alcohols, especially
2-methyl-3-butyn-2-ol and/or 1-ethynyl-2-cyclohexanol which
suppress the activity of a platinum-based catalyst at 25.degree. C.
A second type of platinum catalyst inhibitor is described in U.S.
Pat. No. 3,989,667, which is hereby incorporated by reference to
show certain olefinic siloxanes, their preparation and their use as
platinum catalyst inhibitors. A third type of platinum catalyst
inhibitor includes polymethylvinylcyclosiloxanes having three to
six methylvinylsiloxane units per molecule.
[0052] Compositions containing these catalysts typically require
heating at temperatures of 70.degree. C. or above to cure at a
practical rate. Room temperature cure is typically accomplished
with such systems by use of a two-part system in which the
cross-linker and inhibitor are in one of the two parts and the
platinum is in the other part. The amount of platinum is increased
to allow for curing at room temperature. The optimum concentration
of platinum catalyst inhibitor is that which will provide the
desired storage stability or pot life at ambient temperature
without excessively prolonging the time interval required to cure
the present compositions at elevated temperatures. This amount will
vary widely and will depend upon the particular inhibitor that is
used, the nature and concentration of the platinum-containing
catalyst and the nature of the cross-linker. Inhibitor
concentrations as low as one mole of inhibitor per mole of platinum
will in some instances yield a desirable level of storage stability
and a sufficiently short curing period at temperatures above about
70.degree. C. In other cases, inhibitor concentrations of up to 10,
50, 100, 500 or more moles per mole of platinum may be needed. The
optimum concentration for a particular inhibitor in a given
composition can be determined by routine experimentation.
[0053] Typically, the liquid silicone rubber compositions are
provided as two part compositions. Prior to use, the final liquid
silicone rubber composition as hereinbefore described may be
maintained in at least two parts which can be easily mixed together
in a final mixing step immediately prior to curing the resultant
composition to form an elastomeric solid.
[0054] In a typical two part composition a first part hereafter
referred to as Part I comprises components A.sup.1, A.sup.2,
A.sup.5 and possibly residual treating agent A.sup.3. The second
part, hereafter referred to as Part II, will comprise component
A.sup.4 or components A.sup.4 and A.sup.1. Part I and Part II in a
two part composition may be mixed in any suitable ratio in an
amount such that the ratio of the number of moles of hydrogen atoms
bonded to silicon atoms to the number of moles of alkenyl groups
bonded to silicon atoms is in the range of 0.5:1 to 20:1, or
alternatively in the range of 1:1 to 5:1. Typically, the
cross-linker will be present in the polymer at a level in Part II
such that Part I and Part II will be typically mixed in a ratio of
from 1:10 to 100:1, alternatively 20:1 to 1:5 or alternatively from
10:1 to 1:2.
[0055] Optional additives may be present in either Part I or Part
II providing they do not negatively affect the properties of the
resulting elastomer. Optional additives include rheological
modifiers and adhesion promoters.
[0056] The rheological modifiers include silicone organic
co-polymers such as those described in EP 0802233 based on polyols
of polyethers or polyesters; non-ionic surfactants selected from
the group consisting of polyethylene glycol, polypropylene glycol,
ethoxylated castor oil, oleic acid ethoxylate, alkylphenol
ethoxylates, copolymers or ethylene oxide (EO) and propylene oxide
(PO), and silicone polyether copolymers; as well as silicone
glycols.
[0057] Any suitable adhesion promoter(s) may be incorporated in a
composition in accordance with the present invention. These may
include for example alkoxy silanes such as aminoalkylalkoxy
silanes, epoxyalkylalkoxy silanes, for example,
3-glycidoxypropyltrimethoxysilane and, mercapto-alkylalkoxy silanes
and .gamma.-aminopropyl triethoxysilane, reaction products of
ethylenediamine with silylacrylates. Isocyanurates containing
silicon groups such as 1,3,5-tris(trialkoxysilylalkyl)
isocyanurates may additionally be used. Further suitable adhesion
promoters are reaction products of epoxyalkylalkoxy silanes such as
3-glycidoxypropyltrimethoxysilane with amino-substituted
alkoxysilanes such as 3-aminopropyltrimethoxysilane and optionally
alkylalkoxy silanes such as methyl-trimethoxysilane.
epoxyalkylalkoxy silane, mercaptoalkylalkoxy silane, and
derivatives thereof.
The Stabilizer
[0058] Component B) in the present disclosure is a stabilizer. As
used herein, "stabilizer" refers to a certain combination of
components (B.sup.1, B.sup.2, B.sup.3, and optionally B.sup.4)
added to a curable silicone elastomer composition, such as those
described above, for the purpose of improving either the heat
stability or oil resistance of the subsequently cured silicone
elastomer composition. The stabilizer component comprises; [0059]
B.sup.1) carbon black, [0060] B.sup.2) calcium carbonate, [0061]
B.sup.3) iron oxide, and [0062] B.sup.4) optionally zinc oxide,
each of which are discussed in more detail below.
[0063] Component B.sup.1 is carbon black. The type and source of
carbon black may vary. Representative, non-limiting examples of the
carbon black, useful as component (B.sup.1) in the present
invention can be found in summary articles of this class of
materials such as in: Chemical Economics Handbook-SRI International
2005, Carbon Black 731.3000A. Typically, the carbon black is
amorphous, having a carbon content of at least 98%, an average
particle size of 0.05 micrometers, a specific surface area of at
least 44 m.sup.2/g. Representative, non-limiting examples of carbon
black suitable as component B.sup.1 in the present disclosure
include; SUPERJET.RTM. Carbon Black (LB-1011) supplied by Elementis
Pigments Inc., Fairview Heights, Ill. 62208; SR 511 supplied by Sid
Richardson Carbon Co, 3560 W Market Street, Suite 420, Akron, Ohio
44333; and N330, N550, N762, N990 (Degussa Engineered Carbons,
Parsippany, N.J. 07054).
[0064] Component B.sup.2) is calcium carbonate. The type and source
of calcium carbonate may vary. Representative, non-limiting
examples of the calcium carbonate, useful as component (B.sup.2) in
the present invention can be found in summary articles of this
class of materials such as in: Chemical Economics Handbook-SRI
International 2007, Calcium Carbonate 724.6000A. Typically, the
calcium carbonate is greater than 99% CaCO.sub.3 and the mean
particle size is 5-6 micrometers. Representative, non-limiting
examples of calcium carbonate suitable as component B.sup.2 in the
present disclosure include; OMYA BLP.RTM. 3 (OMYA, Orgon
France).
[0065] Component B.sup.3) is iron oxide. The type and source of
iron oxide may vary. Representative, non-limiting examples of the
iron oxide, useful as component (B.sup.3) in the present invention
can be found in summary articles of this class of materials such as
in: Chemical Economics Handbook-SRI International 2008, inorganic
Color Pigments 575.3000A. Typically, the iron oxide is a micronised
powder containing at least 95% Fe.sub.2O.sub.3 having an average
particle size of 0.2 micrometers, Representative, non-limiting
examples of iron oxide suitable as component B.sup.3 in the present
disclosure include; Baryferrox.RTM. 130 BM (Lanxess Deutschland,
GmbH, D-51369 Leverkusen, Germany)
[0066] Component B.sup.4) is zinc oxide. The type and source of
zinc oxide may vary. Representative, non-limiting examples of the
iron oxide, useful as component (B.sup.4) in the present invention
can be found in summary articles of this class of materials such as
in: Chemical Economics Handbook-SRI International 2007, Inorganic
Zinc Chemicals 798.1000A. Typically, the zinc oxide is at least 99%
ZnO and having an average particle size of 0.1 micrometer, and an
average surface area of 9.0 m.sup.2/g. Representative, non-limiting
examples of zinc oxide suitable as component B.sup.4 in the present
disclosure include;
[0067] Kaddox 911 (Horsehead Corp., Monaca Pa. 15061).
[0068] The amount of each component used in the stabilizer B) may
vary as follows;
B.sup.1) carbon black, 2 to 50 parts, [0069] alternatively, 10 to
40 parts, [0070] alternatively, 25 to 40 parts, [0071] or
alternatively 30 to 35 parts B.sup.2) calcium carbonate, 2 to 50
parts, [0072] alternatively, 10 to 40 parts, [0073] alternatively,
25 to 40 parts, [0074] or alternatively 30 to 35 parts, B.sup.3)
iron oxide, 2 to 50 parts, [0075] alternatively, 10 to 40 parts,
[0076] alternatively, 25 to 40 parts, [0077] or alternatively 30 to
35 parts, B.sup.4) zinc oxide, 0 to 50 parts, [0078] alternatively,
1 to 40 parts, [0079] or alternatively 1 to 10 parts wherein parts
represent the amount of each component by weight B.sup.1, B.sup.2,
B.sup.3, and B.sup.4 in 100 parts by weight of the stabilizer.
[0080] The amount of the stabilizer (that is the total weight of
components B.sup.1, B.sup.2, B.sup.3, and B.sup.4) used in the
curable silicone elastomer composition may vary from 1.5-40 wt %,
alternatively from 5 to 30 wt %, or alternatively from 10 to 20 wt
% of the total curable silicone elastomer composition. The amount
of the stabilizer required for a particular application may be
determined by one skilled in the rubber art based on the selection
of the silicone rubber base (A), the selection of the stabilizer
composition (B), the heat stability requirements and the process
selected for preparing the cured fluorosilicone elastomer. The
stabilizer composition may affect the processibility of the
silicone rubber base. However, techniques to overcome such factors
affecting processibility for added components similar to the
present stabilizers are well known. Such techniques include,
varying concentration, particle shape, and the surface activity of
such components in the silicone elastomer base.
[0081] The manner for how each component of the stabilizer is added
and mixed in the curable silicone elastomer composition may vary.
For example, a mixture of components B.sup.1-B.sup.3 and optionally
B.sup.4 may be first made and admixed to the silicone elastomer
base composition. Alternatively, each individual component may be
added and mixed in any order directly into the curable silicone
elastomer composition. To ensure the most uniform and optimum
mixing, typically a "masterbatch" of each stabilizer component is
prepared by adding the individual stabilizer component with a
portion of the silicone base component. The masterbatched
stabilizer component may then be added to the silicone elastomer
composition. The masterbatch technique is particularly useful for
the addition of carbon black, iron oxide, and zinc oxide.
C) The Cure Agent
[0082] An optional curing agent is added to the silicone elastomer
base containing the stabilizer to effect formation of a cured
silicone elastomer. Typically, curing agents are added to the
silicone elastomer base component in the high consistency silicone
rubber embodiment. Addition of component C) may not be necessary
for the liquid silicone rubber embodiment. Typically, the curing
agents are organic peroxides which are well-known in the silicone
art as curing agents. Specific examples of suitable peroxides which
may be used according to the method of the present invention
include: 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane; benzoyl
peroxide; dicumyl peroxide; t-butyl peroxy O-toluate; cyclic
peroxyketal; t-butyl hydroperoxide; t-butyl peroxypivalate; lauroyl
peroxide; t-amyl peroxy 2-ethylhexanoate; vinyltris(t-butyl
peroxy)silane;
di-t-butyl peroxide, 1,3-bis(t-butylperoxyisopropyl) benzene;
2,2,4-trimethylpentyl-2-hydroperoxide;
2,5-bis(t-butylperoxy)-2,5-dimethylhexyne-3,
t-butyl-peroxy-3,5,5-trimethylhexanoate; cumene hydroperoxide;
t-butyl peroxybenzoate; and diisopropylbenzene mono
hydroperoxide.
[0083] The amount of organic peroxide is not critical. A useful
amount is in a range of 0.1 to 3 weight percent of the silicone
elastomer base containing the stabilizer.
[0084] The curable silicone elastomer compositions may also include
extending fillers, such as titanium dioxide, quartz, magnesium
oxide, graphite, glass fibers and glass microspheres. The silicone
elastomer base may also include pigments, colorants, flame
retardants, additional heat stability additives and additives to
improve compression set.
[0085] In one embodiment, the curable silicone elastomer
composition contains cerium hydroxide or hydrate as optional
component D. The addition of cerium hydroxide or hydrate to
silicone elastomer compositions for heat stabilization is known.
However, such compositions have limited heat stability, typically
to 200.degree. C. The present stabilizer composition (component B)
provides thermal stabilities typically in excess of 200.degree. C.
when used in conjunction with conventional heat stabilizers such as
cerium hydroxide or hydrate. Cerium hydroxide or hydrate useful as
component DA.sup.4 include those cerium compounds having the
formula Ce(OH).sub.4.xH.sub.2O [CAS registry number 12014-56-1].
The amount of cerium hydroxide or hydrate may vary, but typically
ranges from 0.1 to 10 weight % of the silicone elastomer
composition. To ensure the most uniform and optimum mixing,
typically a "masterbatch" of the cerium hydroxide or hydrate
component is prepared by mixing it with a portion of the silicone
base or polydiorganopolysiloxane component. The masterbatched
cerium hydroxide or hydrate component may then be added to the
silicone elastomer composition. Such masterbatched compositions
that are commercially available and useful in the present
compositions include SILASTIC.RTM. HT-1 Modifier (Dow Corning
Corporation, Midland, Mich.).
[0086] The temperature range for curing the silicone elastomer base
may be room temperature or above. A preferred temperature range is
50.degree. C. to 250.degree. C. The temperature range should be
sufficient to activate the catalyst used.
[0087] A silicone elastomer or rubber may be produced by mixing the
silicone base composition detailed above, forming the composition
to a desired configuration, and vulcanizing to yield a silicone
elastomer.
[0088] The silicone elastomeric composition may be formed to the
desired configuration by suitable methods such as compression
molding, injection molding, transfer molding, calendering and
extruding.
[0089] After forming to the desired configuration, the formed
silicone elastomer is vulcanized. When the silicone elastomer
composition contains organic peroxide vulcanizing agent, the
composition is vulcanized by heating to a temperature sufficiently
high to activate the organic peroxide catalyst. When molding, the
temperature is typically from 100.degree. C. to 180.degree. C. for
times of 15 minutes or less. When curing in hot air, as in an
extruding operation, the air temperature may be as high as
300.degree. C. with exposure times as short as 10 to 60
seconds.
[0090] The silicone elastomer exhibits improved retention of
physical properties after aging at elevated temperatures.
[0091] In one embodiment, the cured silicone elastomer has a
tensile strength of at least 7 MPa and an elongation of at least
200%.
[0092] In one embodiment, the tensile strength of the cured
silicone elastomer decreases by no more than 25 percent upon heat
aging of the cured silicone elastomer for 7 days at 225.degree.
C.
[0093] The cured elastomer compositions are useful in a variety of
applications to construct various articles of manufacture
illustrated by but not limited to; O-rings, gaskets, connectors,
seals, liners, hoses, tubing, diaphragms, boots, valves, belts,
blankets, coatings, rollers, molded goods, extruded sheet, caulks,
and extruded articles, for use in applications areas which include
but not are limited to transportation including automotive,
watercraft, and aircraft; chemical and petroleum plants;
electrical: wire and cable: food processing equipment; nuclear
power plants; aerospace; medical applications; and the oil and gas
drilling industry and other applications
EXAMPLES
[0094] These examples are intended to illustrate the invention to
one of ordinary skill in the art and should not be interpreted as
limiting the scope of the invention set forth in the claims. All
measurements and experiments were conducted at 23.degree. C.,
unless indicated otherwise.
Materials Used
TABLE-US-00001 [0095] Material name Description New GP 600 A
silicone rubber base marketed by Dow Corning Corporation (Midland,
MI) as Silastic .RTM. New GP 600. New HGS 701 A silicone rubber
base marketed by Dow Corning Corporation (Midland, MI) as Silastic
.RTM. New HGS 701. HT-1 MB HT-1 MB is a masterbatch of 50% cerium
hydroxide in a dimethyl silicone rubber carrier and is marketed by
Dow Corning Corporation (Midland, MI) as Silastic .RTM. HT-1
Modifier. FeO3 MB S 2400 Red 2 MB - a masterbatch of 50% iron
oxide, as Bayferrox 130 BM Red Iron Oxide Pigment (Lanxess Corp.),
in a dimethyl silicone rubber carrier and is marketed by Dow
Corning Silastic .RTM. S2400 Red 2 Colour Masterbatch. Dicup 40C
Dicumyl peroxide, 40% on CaCO3 GEO Specialty Chemicals ZnO Zinc
oxide as Kaddox 911 (Horsehead Corp., Monaca PA 15061) CB Carbon
black used as provided as SUPERJET .RTM. Carbon Black (LB-1011)
from Elementis Pigments Inc., Fairview Heights, IL 62208. CaCO3
Calcium carbonate (CaCO.sub.3) as OMYA BLP .RTM. 3 (OMYA, Orgon
France)
Formulations
[0096] All test formulations included 100 parts of either "New GP
600" or "New HGS 701", 1.0 parts "HT-1" and 1.5 parts Dicup 40C.
Formulations were made containing various combinations of "Kadox
911", "LB-1011", "S 2400 Red 2 MB", and "BLP-3". Baselines, which
did not include any of the additives, were also made so the effects
of the additives could be measured.
Compounding
[0097] All components were weighed using a 2 place laboratory
balance to within 2% of there target weight. All test formulations
were compounded using a laboratory two roll mill. The mill was
unheated and the temperature of all batches made was kept below
50.degree. C. during mixing. The main component of all the test
formulations, either "New GP 600" or "New HGS 701" depending on the
formulation, was added first and allowed to band on the faster
roll. The HT-1 was added first followed by all additives for the
particular formulation and allowed to mix until incorporated. The
material was then cut from the roll, rolled up and fed back through
the rolls to hand again around the roll. The material was then cut
off, fed through, and allowed to band the same way 9 more times.
The material was then fed back into the mill again and allowed to
band. The "Dicup 40C" was then added and allowed to mix until
incorporated. The material was then cut from the roll, rolled up
and fed back through the rolls to band again around the roll. The
material was then cut off, fed through, and allowed to band the
same way 9 more times. The material was then passed through the
mill using a wider nip gap to obtain a continuous sheet of material
approximately 0.100'' thick more suitable for molding.
Molding
[0098] The apparatus used for molding test slabs consisted of two
12''.times.12''.times.0.040'' aluminum backer plates, both covered
with apiece of PTFE fiber reinforced film, and a 12''.times.12''
steel chase with a cavity measuring 10''.times.10''.times.0.075''.
The material, which had previously been sheeted off the mill, was
weighed to assure a proper fill weight for the chase. The material
was first cold pressed and then placed in a press heated to 170 C
for a duration of 10 minutes at a pressure of 2,100 psi. At the end
of the 10 minutes the material would promptly be removed from the
chase and allowed to cool on a cold steel bench. After cooling the
identification number and molding conditions were written on the
slabs and a light coating of talc dusted over the surface to
prevent the slab from sticking to itself or other slabs during
testing.
Test Methods
[0099] All materials were post cured for 4 hours at a temperature
of 200.degree. C. in a circulating hot air oven before testing
Hardness
[0100] Dow Corning Corporate Test Method 0099, based on ASTM D
2240
Tensile strength, Elongation, Modulus
[0101] Dow Corning Corporate Test Method 0137A, based on ASTM D
412
Tear Strength
[0102] Dow Corning Corporate Test Method 1313, based on ASTM D
624
Heat Aging
[0103] Test specimens were prepared as for normal testing. They
were then measured for thickness and hung by end in a pre-heated
circulating hot air oven for the duration of the specified test
period. Specimen were spaced far enough apart to assure good
airflow around all sides of each specimen. Specimens were then
removed, allowed to cool, and tested within 16-48 hrs according to
the tensile and tear methods using the pre-aged thickness for all
property calculations.
TABLE-US-00002 Initials Aged Change Formulation Ten- Mod Mod Ten-
Mod Mod Ten- Mod Mod Weight HCR's used in sile EB 30 100 Duro sile
EB 30 100 Duro sile EB 30 100 Duro loss TCH construction MPa % MPa
MPa ShA MPa % MPa MPa ShA % % % % pts % 7 days/225 C. New GP 600
10.47 470 1.03 1.79 60 6.03 354 1.08 1.85 61 -42 -25 5 3 1 1.27 New
HGS 701 10.22 294 1.84 3.42 73 6.85 195 2.14 4.05 75 -33 -34 16 18
2 1.87 New GP 600, 2 phr CB, 1.16 471 1.07 1.97 61 7.49 389 1.20
2.07 64 -33 -17 12 5 3 1.93 4 phr FeO3 New HGS 701, 2 phr CB, 10.36
282 1.88 3.59 73 7.50 212 2.22 4.18 76 -28 -25 18 17 3 2.13 4 phr
FeO3 New GP 600, 2 phr CB, 10.82 454 1.11 1.96 61 7.25 384 1.24
2.14 65 -33 -15 12 9 4 2.19 4 phr FeO3, 2 phr CaCO3 New HGS 701, 2
phr CB, 7.69 224 1.93 3.56 73 6.96 188 2.34 4.19 77 -10 -16 21 18 4
2.97 4 phr FeO3, 2 phr CaCO3 New GP 600, 4 phr CB, 10.64 440 1.19
2.13 63 7.24 361 1.38 2.40 67 -32 -18 16 13 3 2.90 4 phr FeO3, 4
phr CaCO3 New HGS 701, 4 phr CB, 9.30 242 2.09 4.01 74 7.04 182
2.66 4.64 79 -24 -24 27 16 5 3.93 4 phr FeO3, 4 phr CaCO3 New GP
600, 3.5 phr ZnO, 8.92 379 1.21 2.23 63 6.92 337 1.46 2.60 68 -22
-11 21 17 4 3.18 3.5 phr CB, 1.5 phr CaCO3 New HGS 701, 3.5 phr
ZnO, 8.16 218 2.13 4.04 75 5.96 146 2.70 4.78 79 -27 -33 27 18 4
3.64 3.5 phr CB, 1.5 phr CaCO3 7 days/250 C. New GP 600 10.47 470
1.03 1.79 60 5.34 307 1.27 2.73 64 -49 -35 23 52 4.7 1.27 New HGS
701 10.22 294 1.84 3.42 73 6.31 152 2.60 5.28 79 -38 -48 41 54 6.2
1.87 New GP 600, 2 phr CB, 11.16 471 1.07 1.97 61 5.19 333 1.24
3.30 65 -53 -29 16 68 4.1 1.93 4 phr FeO3 New HGS 701, 2 phr CB,
10.36 282 1.88 3.59 73 6.15 158 2.60 5.54 79 -41 -44 38 54 5.7 2.13
4 phr FeO3 New GP 600, 2 phr CB, 10.82 454 1.11 1.96 61 5.19 318
1.32 4.14 65 -52 -30 19 112 4.3 2.19 4 phr FeO3, 2 phr CaCO3 New
HGS 701, 2 phr CB, 7.69 224 1.93 3.56 73 4.33 87 2.74 6.96 81 -44
-61 42 96 7.7 2.97 4 phr FeO3, 2 phr CaCO3 New GP 600, 4 phr CB,
10.64 440 1.19 2.13 63 5.00 254 1.66 6.33 70 -53 -42 39 197 6.2
2.90 4 phr FeO3, 4 phr CaCO3 New HGS 701, 4 phr CB, 9.30 242 2.09
4.01 74 5.04 120 3.38 9.49 84 -46 -50 62 137 9.8 3.93 4 phr FeO3, 4
phr CaCO3 New GP 600, 3.5 phr ZnO, 8.92 379 1.21 2.23 63 4.15 191
1.67 6.37 71 -53 -50 38 186 7.9 3.18 3.5 phr CB, 1.5 phr CaCO3 New
HGS 701, 3.5 phr ZnO, 8.16 218 2.13 4.04 75 4.35 92 3.24 7.77 83
-47 -58 52 92 8.4 3.64 3.5 phr CB, 1.5 phr CaCO3
* * * * *